1. Field of the Invention
The invention relates to a pressurized water reactor and to controlling its efficiency by the content of boric acid (H.sub.3 BO.sub.3 ) in the cooling medium.
2. Brief Description of Related Art
As is generally known, the strongest activation during operation of nuclear reactors occurs in the insoluble compounds and metal oxides contained in the cooling medium (O.I. Martynov, A.S. Kopylov, "Vodno-chimiceskie Rezimy AES, Sisteny Ich Poddersanija i Kontrolja", Moscow, Energoisdat, 1983, pgs. 49-50).
The determination of the solubility constant of metal oxides has shown that in reactor water, depending on the temperature and the LiOH and KOHconcentration, considerable lower solubility exists for nickel oxide than for oxides of iron, chromium, manganese, cobalt and other oxides under practically the same conditions.
During the reactor operation the nickel oxide becomes the source for forming of .sup.58 Co, one of the most important contaminating radioactive isotopes in reactors mostly made from steel with a high Ni-content.
An increase in solubility of nickel oxide can occur by either increasing the temperature of the medium or by increasing the alkalinity of the cooling medium, by increasing the content of LiOH or KOH. However, an increase in the temperature of the medium by an increased heat release in the core results in a reduction of safety during the operation of the fuel elements (A.S. Kopylov, E.I. Verchovskij "Specvodoocistka na Atomnych Elektrostanceijach", Moscow, "Vysvaja skola", 1988, pg. 109).
The increase of alkalinity of the cooling medium in pressurized water reactors was tested (see report of IAEA, Coolant Technology of Water Reactors, Doc. 0846j, 03.11.91, pgs. 27-29). A maximum of a permissible pH-value of 8 was found and established (with the aid of a hot sample), that due to the formation of certain amounts of oxide radicals, i.e., of radiolysis products of the water, the increase of alkalinity may result in embrittlement of non-rusting steels of which the individual components of the nuclear reactors are made. The permissible alkalinity ranges, in dependency from the H.sub.3 BO.sub.3 amount, are stated in the Report of IAEA "Coolant Technology of Water Reactors" (Doc. 0846j), 03.11.91, pg. 27.
It is an object of the invention to provide a marked increase of the solubility of Ni-oxides and thereby a lowering of the contamination of reactors with .sup.58 Co.